Question

Write an ARM assembly program that checks bit 2 and bit 18 of R0. If the two bits are similar, then R8=R5<<2 (shift R5 left by 2 bits), otherwise clear the least most significant byte of R1.

Answer 1

MOV R3,R0 (Copy data in R0 to R3)

MOV R2,R0 (Copy data in R0 to R2)

AND R3,R3,0x0002 (Isolate bit2)

AND R2,R2,0x0200     (Isolate bit18)

LSR R2,R2,#16 (Shift bit18 to position of bit2)

CMP R3,R2 (Compare bit2, bit18)

MOVEQ R8,R5,LSL #5 (If R3 = R2, R8 = R5 << 5)

B end (Branch to end of program)

AND R1,R1,0xff00 (Clear least significant byte of R1)

end: (End of program)